五轴联动数控加工中的刀具轨迹控制算法

已有的五轴联动数控加工系统往往忽略刀轴矢量插补问题,只是简单地通过对线性轴进行插补、对旋转轴进行跟随的方式来实现刀具轨迹的控制,导致产生非线性误差和刀具碰撞与干涉等问题。为此,提出一种基于刀轴矢量插补的刀具轨迹控制算法。该算法采用大圆弧插补法对加工过程中的刀轴矢量进行控制,同时采用NURBS曲线拟合方法对控制过程中产生的中间点进行处理,并通过对拟合而成的NURBS曲线进行插补来实时计算各运动轴的位置。该算法不仅能够有效地提高五轴联动数控加工的精度,而且可以有效减小数据存储量。仿真和实际加工验证了算法的有效性和实用性,证明算法具有轨迹过渡平稳、非线性误差小的特点。     

论高等工科院校学生的敬业教育

良好的敬业教育是高等工科院校为社会主义现代化建设培养高素质工程人才的有力保证,学校应该从职业感知、品质培养和实践磨练三个方面来切实加强学生敬业精神的培养工作。     

Doppler ultrasonography in successful varicocele surgery

The authors examined 47 patients after operation on account of varicocele by colour flow mapping and Doppler frequency analysis. In addition they evaluated the postoperative finding clinically and examined also the spermiogram. The greatest success of surgical treatment was observed after laparoscopic ligature of the v. spermatica--a success rate of 91% was recorded after this operation. Bernardi's operation was successful in 62%, Paloma's in 56% of the patients. From 18 patients with a pathological spermiogram before operation they observed improvement in 25%.     

A simple but realistic model for laser cladding

A model which takes into account the main phenomena occurring during the laser-cladding process is proposed. For a given laser power, beam radius, powder jet geometry, and clad height, this model evaluates two other processing parameters, namely, the laser-beam velocity and the powder feed rate. It considers the interactions between the powder particles, the laser beam, and the molten pool. The laser power reaching the surface of the workpiece is estimated and, assuming this power is used to remelt the substrate with the clad having been predeposited, the melt-pool shape is computed using a three-dimensional (3-D) analytical model, which produces mmediate results, even on personal computers. The predictions obtained with this numerical model are in good agreement with experimental results. Processing engineers may therefore use this model to choose the correct processing parameters and to establish cladding maps. Formerly Postdoctoral Fellow, Physical Metallurgy Laboratory.     

Interface microstructures in the diffusion bonding of a titanium alloy Ti 6242 to an INCONEL 625

A Ti6242 alloy has been diffusion bonded to a superalloy INCONEL 625. The microstructures of the as-processed products have been analyzed using optical metallography, scanning electron microscope (SEM), and scanning transmission electron microscope (STEM) techniques. The interdiffusion of the different elements through the interface has been determined using energy-dispersive spectroscopy (EDS) microanalysis in both a SEM and a STEM. Several regions around the original interface have been observed. Starting from the superalloy INCONEL 625, first a sigma phase (Cr₄Ni₃Mo₂), followed by several phases like NbNi₃, Ŋ/Ni₃Ti, Cr(20 pct Mo), β Cr₂Ti, NiTi, TiO, TiNi, and Ti₂Ni intermetallics, just before the Ti6242 have been identified. Because the diffusion of Ni in Ti is faster than the diffusion of Ti in the superalloy, a Kirkendall effect was produced. The sequence of formation of the different phases were in agreement with the ternary Ti-Cr-Ni diagram.     

我国软件产业发展需要大举措

目前我国软件产业规模小、人员分散、抗风险能力低下,处于发展的初级阶段,但人才优势与发展册时并存。面对挑战,必须有相应的大举措,如联合、重组、兼并,如多方筹资、加大投入,如强化管理、政策扶植等等,最终做出正确选择。     

Evaluation of Humidity Correction Factor of Disruptive Discharge Voltage of Standard Sphere Air Gaps

The humidity correction method prescribed in the existing IEC standard is based on experimental data obtained under absolute humidity between 5 and 12 g/m³. A discussion on the humidity correction method is needed for higher absolute humidity regions, which is experienced during summer in Japan, and also throughout the year in tropical countries. The effect of absolute humidity on disruptive discharge voltages of standard sphere air gaps has been studied experimentally for several years under conditions of natural humidity, between 2 and 22 g/m³. In the cases of a.c. and lightning impulse voltage application, it was found that the existing IEC humidity correction method seems to be proper for most of the gap spacings studied under absolute humidity up to 22 g/m³. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Phase Equilibrium for the CaO-SiO₂-FeO-P₂O₅ System at 1673K for Dephosphorization With Multi Phase Flux

Development of the efficient hot metal dephosphorization processes during steelmaking process is one of the most essential topics for the production of high grade clean steels. Since the formation of solid solution composed of tricalcium phosphate and dicalcium silicate could obtain a considerable mass transfer of phosphorus from liquid slag into solid phase during hot metal dephosphorization, itcould obviously sustain a high phosphatecapacityof theliquid slag without huge consumption of lime or addition of fluxes, such as fluorite. The above outlines are the main idea of multi phase flux dephosphorization. For the last few decades, many studies have been done towards the scientific principles and the commercial utilization of this technique. However, the reaction mechanism by using multi phase fluxes remains unclear even by now due tolack of evidence. Based on those previous works, providing a reliable and available phase diagram for the fundamental understanding of the reaction mechanism of multi phase flux dephosphorization has become the main purpose of present research. As well known, the CaO-SiO2-FeO-P2O5 slag is the main component of current steelmaking process. Hence the CaO-SiO2-FeO-P2O5 system at equilibrium has been studied at 1673K with low oxygen partial pressure. The solid phase coexisting with liquid flux is approved to be the solid solution composed of CaO, SiO2 and P2O5. Phosphorus distributes mainly in solid solution rather than liquid phase.     

Error Probability for Convolutional Codes with Weight Enumerating Function

The paper introduces the state reduction algorithm and accelerated state reduction algorithm are used to compute the distance weight enumerator(transfer function) T[x,y] of convolutional codes.Next use computer simulation to compare upper bound on the bit error probability on an additive white Gaussian noise (AWGN) for maximum free distance (MFD) codes of previously found and optimum distance spectrum (ODS) codes with rate 1/4,overall constraint length are 5 and 7,respectively. Finally,a method of how to search for good convolutional codes is given.